1. Field of the Invention
The present invention relates to systems and methods for improving objective measurements preceding corrective eye surgery, and, more particularly, to such systems and methods for improving results of corrective laser surgery on the eye.
2. Description of Related Art
Laser-in-situ-keratomileusis (LASIK) is a common type of laser vision correction method. It has proven to be an extremely effective outpatient procedure for a wide range of vision correction prescriptions. The use of an excimer laser allows for a high degree of precision and predictability in shaping the cornea of the eye. Prior to the LASIK procedure, measurements of the eye are made to determine the amount of corneal material to be removed from various locations on the corneal surface so that the excimer laser can be calibrated and guided for providing the corrective prescription previously determined by the measurements. Refractive laser surgery for the correction of astigmatism typically requires that a cylindrical or quasicylindrical ablation profile be applied to the eye. The long axis of this profile must be properly oriented on the eye in order to accurately correct the visual aberration.
An objective measurement of a patient""s eye is typically made with the patient typically sitting in an upright position while focusing on a target image. A wavefront analyzer then objectively determines an appropriate wavefront correction for reshaping the cornea for the orientation of the eye being examined. The LASIK or PRK procedure is then typically performed with the patient in a prone position with the eye looking upward.
It is well known that the eye undergoes movement within the socket comprising translation and rotation (xe2x80x9ccyclotortionxe2x80x9d) as the patient is moved from the upright measuring position to the prone surgery position. Techniques known in the art for accommodating this movement have included marking the eye by cauterizing reference points on the eye using a cautery instrument (U.S. Pat. No. 4,476,862) or caustic substance, a very uncomfortable procedure for the patient. It is also known to mark a cornea using a plurality of blades (U.S. Pat. No. 4,739,761). The injection of a dye or ink is also used to mark the reference locations to identify the orientation of the eye during measurement, permitting a positioning of the corrective profile to the same orientation prior to surgery. However, the time delay from measurement to surgery often causes the ink to run, affecting the accuracy of an alignment. Making an impression on the eye (U.S. Pat. No. 4,705,035) avoids the caustic effects of cauterizing and the running effect of the ink. However, the impression loses its definition quickly relative to the time period between the measurement and surgery.
For correction of astigmatism, it is known to mark the cornea preparatory to making the surgical incisions (U.S. Pat. No. 5,531,753).
Tracker systems used during the surgical procedure or simply for following eye movement, while the patient is in a defined position, are known to receive eye movement data from a mark on a cornea made using a laser beam prior to surgery (U.S. Pat. No. 4,848,340) or from illuminating and capturing data on a feature in or on the eye, such as a retina or limbus, for example (U.S. Pat. Nos. 5,029,220; 5,098,426; 5,196,873; 5,345,281; 5,485,404; 5,568,208; 5,620,436; 5,638,176; 5,645,550; 5,865,832; 5,892,569; 5,923,399; 5,943,117; 5,966,197; 6,000,799; 6,027,216).
It is therefore an object of the present invention to provide a system and method for accurately orienting the eye for surgery.
It is a further object to provide such a system and method that orients the eye to the same orientation it had during an objective measurement.
It is another object to provide such a system and method that avoids placing the patient in an uncomfortable or harmful situation.
It is an additional object to provide such a system and method that provides an orientation correction algorithm to the software driving the corrective surgical device.
It is yet a further object to provide such a system and method that can align (register) pairs of eye images taken at different times.
These and other objects are achieved by the present invention, an orientation system for corrective eye surgery. A first embodiment of the system comprises means for performing a first image mapping an eye of a patient situated in a first position using a predetermined eye feature. Means are further provided for performing a second image mapping of the eye of the patient in a second position different from the first position using the predetermined eye feature. Means are also provided for processing the first and the second image map to determine an edge location of the feature in two dimensions and to locate the predetermined eye feature. Finally, software means are included for calculating an orientational change to be applied to a corrective prescription for a surgical procedure to be performed on the eye with the patient in the second position. The procedure may comprise, for example, a correction profile that had been determined with the patient in the first position with, for example, a wavefront analysis and conversion system for calculating an ablation profile for a cornea, such as described in copending and co-owned application Ser. No. 09/566,668, the disclosure of which is hereby incorporated by reference.
The method of this first embodiment of the present invention is for orienting a corrective program for eye surgery and comprises the steps of performing a first image mapping of an eye of a patient in a first position using a predetermined eye feature. The method also comprises the steps of performing a second image mapping of the eye of the patient in a second position different from the first position using the feature and processing the first and the second image map to determine an edge location of the feature in two dimensions and to locate the feature. Next an orientational change to be applied to a corrective prescription for a surgical procedure to be performed on the eye with the patient in the second position is calculated. The procedure comprises a correction profile determined with the patient in the first position.
Thus this aspect of the present invention provides a system and method for achieving a precise registration of the eye with a measurement of the movement of an eye feature. As a result, the prescription measurement for reshaping the cornea will account for the rotation and translation of the eye occurring between measurements made with the patient in a sitting position and laser surgery with the patient in a prone position.
A second orientation system for eye surgery for correcting astigmatism comprises means for making two alignment marks on an eye of a patient with the patient in a first position. Means are also provided for imaging the eye with the patient in a second position that is different from the first position. The system also comprises a computer that has input and output means. The input means are in electronic connection with the imaging means, and an operator input device is in electronic communication with the computer input means. Means are also in communication with the computer input and output means for displaying the eye image to an operator.
First software means are resident in the computer for superimposing a graphical reticle means onto the eye image on the displaying means and for permitting the graphical reticle means to be moved by the operator under control of the operator input means. The reticle means comprise a line for aligning with the two alignment marks. Second software means also resident in the computer are for calculating an orientational change to be applied to a corrective surgical procedure to be performed on the eye with the patient in the second position. As above, the procedure comprises a correction profile determined with the patient in the first position.
The features that characterize the invention, both as to organization and method of operation, together with further objects and advantages thereof, will be better understood from the following description used in conjunction with the accompanying drawing. It is to be expressly understood that the drawing is for the purpose of illustration and description and is not intended as a definition of the limits of the invention. These and other objects attained, and advantages offered, by the present invention will become more fully apparent as the description that now follows is read in conjunction with the accompanying drawing.